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Artificial Cloud Test Confirms Volcanic Ash Detection Using Infrared Spectral Imaging


Artificial Cloud Test Confirms Volcanic Ash Detection Using Infrared Spectral Imaging

A J Prata et al. Sci Rep.


Airborne volcanic ash particles are a known hazard to aviation. Currently, there are no means available to detect ash in flight as the particles are too fine (radii < 30 μm) for on-board radar detection and, even in good visibility, ash clouds are difficult or impossible to detect by eye. The economic cost and societal impact of the April/May 2010 Icelandic eruption of Eyjafjallajökull generated renewed interest in finding ways to identify airborne volcanic ash in order to keep airspace open and avoid aircraft groundings. We have designed and built a bi-spectral, fast-sampling, uncooled infrared camera device (AVOID) to examine its ability to detect volcanic ash from commercial jet aircraft at distances of more than 50 km ahead. Here we report results of an experiment conducted over the Atlantic Ocean, off the coast of France, confirming the ability of the device to detect and quantify volcanic ash in an artificial ash cloud created by dispersal of volcanic ash from a second aircraft. A third aircraft was used to measure the ash in situ using optical particle counters. The cloud was composed of very fine ash (mean radii ~10 μm) collected from Iceland immediately after the Eyjafjallajökull eruption and had a vertical thickness of ~200 m, a width of ~2 km and length of between 2 and 12 km. Concentrations of ~200 μg m(-3) were identified by AVOID at distances from ~20 km to ~70 km. For the first time, airborne remote detection of volcanic ash has been successfully demonstrated from a long-range flight test aircraft.

Conflict of interest statement

The authors declare no competing financial interests.


Figure 1
Figure 1
(a) Photograph taken from the A340 showing the A400M dispensing ash into the atmosphere. The DA42 can also be seen sampling part of the dispersing ash layer. (b) Locations of the A340 aircraft runs. The track of the A400M, dispensing the ash, is shown as a red solid line; the A340 tracks are shown as broken lines and colour coded as follows: blue = run 1, flight level 150 (15,000 ft); yellow = run 2, flight level 100 (10,000 ft); orange = run 3, flight level 050 (5,000 ft); green = run 4, flight level 050. The arrows indicate the direction of travel of the aircraft. The grey-coloured thick-dashed lines show the approximate horizontal field-of-view of the AVOID cameras. Inset map shows the geographic location of the experiment. (c) Satellite image (MODIS/Aqua: acquired ~30 minutes after the ash was first inserted into the atmosphere. The ash layer was not detectable at the spatial resolution (250 m) of the visible channels of the MODIS instrument. The map was drawn using the IDL v8.2 software package ( The MODIS data are courtesy of NASA/GSFC and processed using IDL v8.2.
Figure 2
Figure 2
(a) Ash signal observed by the dual infrared camera imaging system, AVOID on board the A340 test aircraft from 5000 ft (FL050) viewing the ash cloud at ~11,000 ft from distances of ~70 km. The vertical field-of-view of the system is shown as the hatched coloured region, the A340 altitude is constant at 5000 ft, while the pitch of the instrument (shown in red) undergoes small changes. The total time interval is ~8 minutes. The ash signal is shown in shades of yellow (weaker signal) and orange (stronger signal). The solid vertical line at 10:58 UT corresponds to the time when the DA42 was sampling inside the ash cloud and a vertical profile at this time is shown in Fig. 3(a). (b) A single AVOID image frame showing the ash detection signal (yellow/orange) and coincident ash concentrations measured by the DA42 (filled circles). The background shows brightness temperatures from the reference channel in shades of blue to white (cold to warm). (c) Ash signal (in %; filled circles) as a function of distance (km) from the ash cloud, shown for two flight runs. The signal is defined as the ratio of the number of pixels identified as ash to the total number of pixels, expressed as a percentage. The solid blue curve shows a theoretical detection limit based on the geometry of the cloud, the pixel resolution (distance dependent) and perfect detection of ash regardless of the amount. The difference between the measured signal and the theoretical estimates is shown every 5 km (black circles) with the standard deviation over 5 km also shown. Beyond 25 km the difference is at or below 1%.
Figure 3
Figure 3
(a) AVOID measurements at two times: 10:58:00 UTC when the DA42 aircraft had descended below the ash layer, and 11:15:37 UTC when the DA42 was flying within the ash layer. The ash layer was thin (<300 m deep) and multilayered. (b) Histogram of the mass concentration measured by the OPC showing a peak at around ~70 μg m−3 representing the background particulate concentration and a broader peak between 250 and 450 μg m−3 representing the ash layer concentration. (c) In situ OPC measurements of the airborne ash made during the experiment. The upper line shows the altitude of the DA42 aircraft, with colours representing the particle mass concentration. Particle mass concentration (mg m−3) is plotted as a function of time for a period when the AVOID system was viewing the ash layer. Between 10:50 and 11:00 UTC the aircraft descended until negligible particles could be counted, and the layer depth at this time is estimated to be ~280 m. Over a period of ~1 hour the mean concentration dropped from 1200 to 450 μg m−3.
Figure 4
Figure 4
(a) Energy Dispersive X-ray Spectroscopic (EDS) elemental map of the Eyjafjallajökull ash sample. The influence of water during fragmentation has resulted in the blocky and irregular shapes of the particles. (b) A magnified portion of the image showing the highly complex mixture of elements contained in the various crystalline and glassy structures. The colours represent counts of each of the following elements in order of abundance: red = Si, blue = Al, green = Fe, yellow = Ca, magenta = K, and cyan = Ti. The crystals dominated by Ca (yellow) are Ca-rich pyroxene (augite), crystals dominated by Fe and Ti (green and cyan) are ilmenite, crystals highlighted by a lack of Ca (yellow) and presence of Al (blue) and K (magenta) are most likely a Al-K-rich plagioclase (orthoclase). These crystals are set in an amorphous groundmass of glass. (c) Spectrum of counts per second per electron volt. These energies allow identification of elements and their semi-quantitative proportions.

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